[ male announcer ] get a new kindle fire hd, plus a free custom cover, and a free $25 amazon.com gift card. this is a limited-time offer, and you won't find it anywhere else. kindle fire is amazing. it's a life-changer. [ male announcer ] go online to order now. from new york city, this is "nightline" with cynthia mcfadden. good evening, and thank you for joining us, we begin with a terrifying event in atlanta today, screaming children flooding out of their elementary school. a gunman inside with a weapon, a scene harkening back to the tragedy that happened in newtown, connecticut. today, thankfully, no one was hurt. but as children all over the country head back to school, questions abound.